"Well, I go to ceneo.pl (possibly the most popular and well-known here catalogue of products and online shops), to 'laptops' category (noting that a laptop without an OS is the most popular one), pick 'no OS' and 'Linux' options, and..."

I visited the link to verify your claim, but I cannot read it so I'll take you at your word. If it is the case that no-os is the most popular option there, it makes me wonder how many people are not getting what they really want when there isn't a no-os choice.

Heck, not even talking in terms of alternate OS, some people might routinely be overwriting a bundled copy of windows home with a standalone copy of windows professional, because no-os isn't a choice. I'm sure a good chunk of windows sales go to customers who'd rather buy windows licenses separately and reuse it if no-OS systems were easier to buy. I'm really curious as to how often bundled windows licenses are oversold like this.